U.S. patent application number 14/287978 was filed with the patent office on 2015-12-03 for inductor current measurement compensation for switching voltage regulators.
The applicant listed for this patent is Infineon Technologies Austria AG. Invention is credited to Amir Babazadeh, Tim Ng, Benjamim Tang, Darryl Tschirhart.
Application Number | 20150349634 14/287978 |
Document ID | / |
Family ID | 54481605 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150349634 |
Kind Code |
A1 |
Tschirhart; Darryl ; et
al. |
December 3, 2015 |
INDUCTOR CURRENT MEASUREMENT COMPENSATION FOR SWITCHING VOLTAGE
REGULATORS
Abstract
A current estimation method for a switching voltage regulator
that delivers current to a load through an inductor includes
measuring a voltage across a capacitor of an RC current sense
network coupled in parallel with the inductor, generating an
estimate of the current through the inductor based on the voltage
measured across the capacitor of the RC current sense network and
adjusting the estimate of the current through the inductor by a
compensation filter that compensates for variation in the
inductance of the inductor as a function of at least one of
temperature and current.
Inventors: |
Tschirhart; Darryl;
(Torrance, CA) ; Tang; Benjamim; (Rancho Palos
Verdes, CA) ; Babazadeh; Amir; (Laguna Hills, CA)
; Ng; Tim; (Monterey Park, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies Austria AG |
Villach |
|
AT |
|
|
Family ID: |
54481605 |
Appl. No.: |
14/287978 |
Filed: |
May 27, 2014 |
Current U.S.
Class: |
323/271 ;
702/64 |
Current CPC
Class: |
H02M 2001/0009 20130101;
H02M 3/156 20130101; G01R 19/32 20130101; H02M 3/158 20130101; G01R
19/25 20130101 |
International
Class: |
H02M 3/158 20060101
H02M003/158; G01R 19/32 20060101 G01R019/32 |
Claims
1. A method of current estimation for a switching voltage regulator
that delivers current to a load through an inductor, the method
comprising: measuring a voltage across a capacitor of an RC current
sense network coupled in parallel with the inductor; generating an
estimate of the current through the inductor based on the voltage
measured across the capacitor of the RC current sense network; and
adjusting the estimate of the current through the inductor by a
compensation filter that compensates for variation in the
inductance of the inductor as a function of at least one of
temperature and current.
2. The method of claim 1, further comprising measuring a
temperature of the switching voltage regulator, wherein the RC
current sense network accounts for the DCR (non-ideal DC
resistance) of the inductor and the compensation filter compensates
for temperature variation between the DCR and inductance of the
inductor as a function of the measured temperature, the
compensation filter comprising a plurality of filter coefficients
that are a function of the measured temperature.
3. The method of claim 2, further comprising: calculating a first
one of the plurality of filter coefficients as a function of a time
constant (.tau..sub.C) for the RC current sense network, a time
constant (.tau..sub.L) for the inductor and a temperature parameter
(.DELTA..sub.T) that is a function of the difference between the
measured temperature and a temperature at which the DCR of the
inductor is specified; and calculating a second one of the
plurality of filter coefficients as a function of .tau..sub.L,
.DELTA..sub.T and a sampling frequency at which the estimate of the
current through the inductor is generated.
4. The method of claim 3, further comprising: calculating
.DELTA..sub.T=.alpha.(T-T.sub.0) where .alpha. is a temperature
coefficient of resistivity for the inductor, T is the measured
temperature and T.sub.0 is the temperature at which the DCR of the
inductor is specified.
5. The method of claim 2, wherein the measured temperature is used
to compensate for the temperature variation between the DCR and
inductance of the inductor during transient load conditions.
6. The method of claim 2, further comprising providing
over-temperature protection for the switching voltage regulator
based on the same measured temperature used to compensate for the
temperature variation between the DCR and inductance of the
inductor.
7. The method of claim 1, wherein the RC current sense network
accounts for the DCR (non-ideal DC resistance) of the inductor and
the compensation filter compensates for a current-dependency of the
inductance of the inductor, the compensation filter comprising a
plurality of filter coefficients that are a function of the
current-dependency of the inductance.
8. The method of claim 7, further comprising: calculating a first
one of the plurality of filter coefficients as a function of a time
constant (.tau..sub.C) for the RC current sense network and a time
constant (.tau..sub..DELTA.I) for the inductance of the inductor as
a function of current through the inductor; and calculating a
second one of the plurality of filter coefficients as a function of
.tau..sub..DELTA.I and a sampling frequency at which the estimate
of the current through the inductor is generated.
9. The method of claim 8, further comprising: calculating
.tau..sub..DELTA.I=L(I)/DCR and L(I)=m.sub.LI+L.sub.b where L(I) is
an estimate of the inductance as a function of current, DCR is the
DC resistance of the inductor, m.sub.L is a slope of decrease for
the inductance as a function of current, I is current, and L.sub.b
is an intercept of an extrapolated slope for the inductance versus
current.
10. The method of claim 9, wherein the compensation filter assumes
a linear decrease m.sub.L.
11. The method of claim 9, further comprising disabling the
compensation filter over a range of the inductor current for which
m.sub.L is relatively flat.
12. A controller for controlling operation of a switching voltage
regulator that delivers current to a load through an inductor, the
controller comprising: an RC current sense network coupled in
parallel with the inductor; a current estimator operable to
generate an estimate of the current through the inductor based on a
voltage measured across the capacitor of the RC current sense
network; and a compensation filter operable to adjust the estimate
of the current through the inductor by compensating for variation
in the inductance of the inductor as a function of at least one of
temperature and current.
13. The controller of claim 12, further comprising a temperature
sensor operable to measure a temperature of the switching voltage
regulator, wherein the RC current sense network accounts for the
DCR (non-ideal DC resistance) of the inductor and the compensation
filter is operable to compensate for temperature variation between
the DCR and inductance of the inductor as a function of the
measured temperature, the compensation filter comprising a
plurality of filter coefficients that are a function of the
measured temperature.
14. The controller of claim 13, wherein: a first one of the
plurality of filter coefficients is calculated as a function of a
time constant (.tau..sub.C) for the RC current sense network, a
time constant (.tau..sub.L) for the inductor and a temperature
parameter (.DELTA..sub.T) that is a function of the difference
between the measured temperature and a temperature at which the DCR
of the inductor is specified; and a second one of the plurality of
filter coefficients is calculated as a function of .tau..sub.L,
.DELTA..sub.T and a sampling frequency at which the estimate of the
current through the inductor is generated.
15. The controller of claim 14, wherein
.DELTA..sub.T=.alpha.(T-T.sub.0), .alpha. is a temperature
coefficient of resistivity for the inductor, and T is the measured
temperature and T.sub.0 is the temperature at which the DCR of the
inductor is specified.
16. The controller of claim 13, further comprising an
over-temperature protection circuit operable to provide
over-temperature protection for the switching voltage regulator
based on the same measured temperature used to compensate for the
temperature variation between the DCR and inductance of the
inductor.
17. The controller of claim 13, wherein a time constant of the RC
current sense network does not match the time constant of the
inductor and the DCR of the inductor at nominal conditions.
18. The controller of claim 12, wherein the RC current sense
network accounts for the DCR (non-ideal DC resistance) of the
inductor and the compensation filter is operable to compensate for
a current-dependency of the inductance of the inductor, the
compensation filter comprising a plurality of filter coefficients
that are a function of the current-dependency of the
inductance.
19. The controller of claim 18, wherein: a first one of the
plurality of filter coefficients is calculated as a function of a
time constant (.tau..sub.C) for the RC current sense network and a
time constant (.tau..sub..DELTA.I) for the inductance of the
inductor as a function of current through the inductor; and a
second one of the plurality of filter coefficients is calculated as
a function of .tau..sub..DELTA.I and a sampling frequency at which
the estimate of the current through the inductor is generated.
20. The controller of claim 19, wherein .tau..sub..DELTA.I=L(I)/DCR
and L(I)=m.sub.LI+L.sub.b, L(I) is an estimate of the inductance as
a function of current, DCR is the DC resistance of the inductor,
m.sub.L is a slope of decrease for the inductance as a function of
current, I is current, and L.sub.b is an intercept of an
extrapolated slope for the inductance versus current.
21. The controller of claim 20, wherein the controller is further
operable to disable the compensation filter over a range of the
inductor current for which m.sub.L is relatively flat.
22. A multiphase switching voltage regulator, comprising: a
plurality of phases operable to deliver current to a load, each
phase being connected to the load through an inductor; an RC
current sense network coupled in parallel with each of the
inductors; a current estimator operable to generate an estimate of
the individual currents through the inductors based on a voltage
measured across the capacitors of the RC current sense networks,
and generate a total current estimate based of the individual
current estimates for the inductors; and a compensation filter
operable to adjust the total current estimate by compensating for
variation in the inductance of the inductors as a function of at
least one of temperature and current.
Description
TECHNICAL FIELD
[0001] The present application relates to switching voltage
regulators, in particular inductor current measurement compensation
for switching voltage regulators.
BACKGROUND
[0002] Switching voltage regulators are widely used in modern
electronic systems for a variety of applications such as computing
(server and mobile) and POLs (Point-of-Load Systems) for
telecommunications because of their high efficiency and small
amount of area/volume consumed by such converters. Widely accepted
switching voltage regulator topologies include buck, boost,
buck-boost, forward, flyback, half-bridge, full-bridge, and SEPIC
topologies. Multiphase buck converters are particularly well suited
for providing high current at low voltages needed by
high-performance integrated circuits such as microprocessors,
graphics processors, and network processors. Buck converters are
implemented with active components such as a pulse width modulation
(PWM) controller IC (integrated circuit), driver circuitry, one or
more phases including power MOSFETs (metal-oxide-semiconductor
field-effect transistors), and passive components such as
inductors, transformers or coupled inductors, capacitors, and
resistors. Multiple phases (power stages) can be connected in
parallel to the load through respective inductors to meet high
output current requirements.
[0003] Accurate knowledge of the current being supplied by a
switching voltage regulator is required for safe, robust operation.
Incorrect current measurement can lead to premature tripping
over-current protection (OCP), which is undesirable in
high-reliability applications such as servers in data centers, or
failure to trip OCP which can lead to catastrophic device failure.
In either case, incorrect current information causes an incorrect
output voltage set point that may be out of compliance with product
specifications.
[0004] The standard technique for ascertaining the current through
an inductor in a switching voltage regulator is known as DCR
sensing which exploits the non-ideal DC resistance (DCR) of the
inductor. The DCR of an inductor is specified at nominal conditions
in the datasheet for off-the-shelf components, or may be calculated
or measured in custom designs. With DCR sensing, a
resistor-capacitor (RC) sense network is connected in parallel with
the inductor and the voltage across the capacitor represents the
voltage across the DCR, meaning the current through the inductor is
related to the ratio of the capacitor voltage to DCR value. For a
static, DC current through the load, the DC value across the
capacitor is proportional to the DC current through the inductor
and the DCR of the inductor. For dynamic currents, such as a
changing current through the load or a ripple current through the
inductor, the instantaneous value across the capacitor is
proportional to the instantaneous current through the inductor if
the time constant of the RC network matches that of the inductance
and DCR of the inductor. However, inductance and DCR vary with
temperature, meaning the current information is only accurate at
the temperature where the time constants match.
[0005] Many conventional switching voltage regulators use a
negative temperature coefficient thermistor (NTC) network to
augment the DCR measurement. The NTC network for DCR compensation
typically is separate from the NTC network for over temperature
protection (OTP), increasing overall system cost, component count
and signal routing complexity. In addition, the temperature
compensation NTC network does not contain useful information.
Instead, the temperature compensation NTC network is a manually
tuned unintelligent network. As a result, the network is specific
to the platform on which it is used. Changing design parameters
with thermal implications (e.g. board layer count, air flow,
components with lower efficiency, etc.) require a hardware change
to re-tune the NTC network. Also, component tolerances of the NTC
network introduce additional error in the current measurement and
the NTC technique for DCR compensation is only viable for DC
measurements. As such, the dynamic or AC value of current is
uncompensated.
SUMMARY
[0006] According to an embodiment of a method of current estimation
for a switching voltage regulator that delivers current to a load
through an inductor, the method comprises: measuring a voltage
across a capacitor of an RC current sense network coupled in
parallel with the inductor; generating an estimate of the current
through the inductor based on the voltage measured across the
capacitor of the RC current sense network; and adjusting the
estimate of the current through the inductor by a compensation
filter that compensates for variation in the inductance of the
inductor as a function of at least one of temperature and
current.
[0007] According to an embodiment of a controller for controlling
operation of a switching voltage regulator that delivers current to
a load through an inductor, the controller comprises an RC current
sense network coupled in parallel with the inductor, a current
estimator and a compensation filter. The current estimator is
operable to generate an estimate of the current through the
inductor based on a voltage measured across the capacitor of the RC
current sense network. The compensation filter is operable to
adjust the estimate of the current through the inductor by
compensating for variation in the inductance of the inductor as a
function of at least one of temperature and current.
[0008] According to an embodiment of a multiphase switching voltage
regulator, the multiphase switching voltage regulator comprises a
plurality of phases operable to deliver current to a load, each
phase being connected to the load through an inductor, an RC
current sense network coupled in parallel with each of the
inductors, a current estimator, and a compensation filter. The
current estimator is operable to generate an estimate of the
individual currents through the inductors based on a voltage
measured across the capacitors of the RC current sense networks,
and generate a total current estimate based of the individual
current estimates for the inductors. The compensation filter is
operable to adjust the total current estimate by compensating for
variation in the inductance of the inductors as a function of at
least one of temperature and current.
[0009] Those skilled in the art will recognize additional features
and advantages upon reading the following detailed description, and
upon viewing the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0010] The elements of the drawings are not necessarily to scale
relative to each other. Like reference numerals designate
corresponding similar parts. The features of the various
illustrated embodiments can be combined unless they exclude each
other. Embodiments are depicted in the drawings and are detailed in
the description which follows.
[0011] FIG. 1 illustrates a block diagram of an embodiment of a
multiphase switching voltage regulator having inductor DCR current
sense with compensation.
[0012] FIG. 2 illustrates a flow diagram of an embodiment of a
method of compensation for a switching voltage regulator having
inductor DCR current sense.
[0013] FIG. 3 illustrates a block diagram of an embodiment of a
compensation filter that provides temperature compensation to a
multiphase switching voltage regulator with inductor DCR current
sense.
[0014] FIG. 4 illustrates a block diagram of an embodiment of a
compensation filter that provides current-dependency compensation
to a multiphase switching voltage regulator with inductor DCR
current sense.
[0015] FIG. 5 illustrates a plot diagram showing the
current-dependency of the inductance of an inductor of a multiphase
switching voltage regulator.
DETAILED DESCRIPTION
[0016] Embodiments described herein provide DCR-based current
estimation techniques that compensate for variation between the DCR
and phase inductance. In some embodiments, actual temperature
readings for the switching voltage regulator are used to implement
the current estimate compensation. The same temperature measurement
used to compensate the DCR-based current estimation process can
also be used in over-current and over-temperature protection
processes. In other embodiments, the current-dependency of the
phase inductance is used to implement the current estimate
compensation. Still other types of compensation can be used such as
voltage or frequency compensation. In each case, both steady-state
(DC) and transient (AC) load conditions can be mitigated based on
the current estimate compensation techniques described herein by
using a compensation filter that has a non-constant frequency
response.
[0017] FIG. 1 illustrates an embodiment of a switching voltage
regulator 100 comprising a power stage 102 including a plurality of
phases 104 and a controller 106 such as a microcontroller,
microprocessor, ASIC (application-specific integrated-circuit),
etc. for controlling operation of the power stage 102. Each phase
104 is operable to deliver a phase current (I.sub.Ln) through a
separate inductor (L.sub.O) to a load connected to the switching
voltage regulator 100 via the inductors and an output capacitor
(C.sub.O). The load can be a high-performance integrated circuit
such as a microprocessor, graphics processor, network processor,
etc. or other type of integrated circuit requiring voltage
regulation such as a POL (point-of-load). The load is represented
by resistor R.sub.L in FIG. 1.
[0018] Each phase 104 has a high-side transistor (Q1) and a
low-side transistor (Q2) for coupling to the load through the
corresponding inductor. The high-side transistor of each phase 104
switchably connects the load to an input voltage (Vin) of the
switching voltage regulator 100, and the corresponding low-side
transistor switchably connects the load to ground at different
periods. N phases are shown in FIG. 1. The power stage 102 can
include any number of phases including a single phase or more than
one phase.
[0019] The controller 106 regulates the voltage (V.sub.O) delivered
to the load by the power stage 102, by adjusting the phase currents
delivered to the load. The controller 106 can include a pulse width
modulator (PWM) 108 for switching each phase 104 of the power stage
102 via a corresponding PWM control signal (PWM1, PWM2, . . . ,
PWMn) so that the power stage 102 sources or sinks current to the
load through the corresponding inductor and the high-side or
low-side transistor. When the PWM control signal is at a logic
level high, the high-side transistor is placed in a conductive
state, the inductor current is sourced or sunk through the
high-side transistor, and the current through the inductor
increases for the duration. This is generally referred to as the
`on-time` and the power stage 102 is considered to be `turned on`.
When the PWM control signal is at a logic level low, the low-side
transistor is placed in a conductive state, current is sourced or
sunk from the low-side transistor, and the current through the
inductor decreases for the duration. This is generally referred to
as the `off-time` and the power stage 102 is considered to be
`turned off`. When the PWM control signal is at a trivalent or high
impedance logic level (the PWM control signal is neither high nor
low), both the high-side and the low-side transistors are placed in
a non-conductive state, current is sourced or sunk through either
the low-side or high side transistor body diodes, and the magnitude
of the current through the inductor decreases towards zero. This is
generally referred to as the `HiZ-time` or `inactive time` and the
power stage 102 is considered to be in `High Z` or inactive.
[0020] The switching voltage regulator 100 can source or sink
current, and each inductor current has an expected sawtooth or
triangular shape or ripple pattern, since the inductor currents
must be either decreasing or increasing depending on which
transistor is conductive. In DCM (discontinuous conduction mode),
the low-side transistor is not allowed to be conductive when the
inductor current is zero. The cycle then consists of an on-time,
followed by an off-time, followed by a HiZ time. During the HiZ
time, the inductor current approaches zero and does not change for
the duration of the cycle once it is near zero.
[0021] In either CCM or DCM, drivers 110 of the power stage 102
provide gate drive signals to the gates of the high-side and
low-side transistors of the corresponding phases 104 in response to
the PWM control signals provided by the controller 106. The
activation state of the phases 104 and the duty cycle of the
high-side and low-side transistors are determined at least in part
based on the output voltage (V.sub.O) applied to the load so that
the switching voltage regulator 100 can react as quickly and
reliably as possible to changing load conditions.
[0022] The controller 106 can manage changes from one reference
voltage to another. The controller 106 can also determine errors
between the output voltage (V.sub.O) and a reference voltage, and
convert the error voltage into a digital representation provided to
the PWM 108 for modifying the switching cycle of the phases 104
e.g. by adjusting the duty cycle. Such voltage regulation functions
are standard in typical digitally-controlled switching voltage
regulators, and therefore no further explanation is given in this
regard.
[0023] In addition to regulating the voltage delivered to the load,
the controller 106 also monitors the phase currents delivered by
the phases 104 to the load e.g. by measuring the phase currents
(I.sub.Ln) injected into the corresponding inductors by DCR
sensing. The controller 106 estimates the total current delivered
to the load by the switching voltage regulator 100 based on the
phase currents measured by DCR sensing.
[0024] The current estimation method implemented by the switching
voltage regulator controller 106 is explained next in more detail
with reference to FIG. 2. The power stage 102 of the switching
voltage regulator 100 includes an RC current sense network 112
coupled in parallel with each phase 104. The RC current sense
network 112 includes a resistor (R.sub.sen) connected in series
with a capacitor (C.sub.sen). The RC current sense network 112
accounts for the DCR (non-ideal DC resistance) of the inductor. The
voltage (V.sub.Cn) measured across the capacitor (C.sub.sen)
represents the voltage across the DCR of that inductor, meaning the
current (I.sub.Ln) through the inductor is related to the ratio of
the capacitor voltage to DCR value (Block 200).
[0025] The controller 106 includes a current sensor 114 generating
an estimate of the current through each inductor based on the
voltage (V.sub.C1, V.sub.C2, . . . V.sub.Cn) measured across the
capacitors of the respective RC current sense networks (Block 210).
In one embodiment, the controller 106 is a digital controller and
the current sensor 114 comprises an ADC (analog-to-digital
converter) 116 for converting the individual voltages (V.sub.C1,
V.sub.C2, . . . V.sub.Cn) measured by the DCR sense networks 112 to
a corresponding digital value. The digitized values output by the
ADCs 116 represent the individual phase current estimates, which
are summed 118 to provide a digitized total current estimate
(I.sub.T). In the case of a single-phase switching voltage
regulator, the regulator includes only one output inductor (L) and
the summing stage 118 can be omitted. In this case, the digitized
total current estimate I.sub.T shown in FIG. 1 is the current
estimate determined for the single inductor.
[0026] The controller 106 includes a compensation filter 120 for
adjusting the estimate of the digitized total current estimate
I.sub.T (Block 220). According to the embodiment of FIG. 1, the
compensation filter 120 is a temperature compensation filter that
compensates for variation in the DCR of the inductors as a function
of temperature. To this end, the switching voltage regulator 100
also includes a temperature sensor 122 for measuring the
temperature of the switching voltage regulator 100. The temperature
sensor 122 can be placed at or near the power stage 102 if desired.
Any standard temperature sensor that outputs a voltage, current, or
resistance that varies with temperature and that can be converted
to an actual temperature reading can be employed. Again in the case
of a digital architecture, the controller 106 can include an ADC
124 for converting the measured temperature reading to a
corresponding digitized value (T). The controller 106 uses the
measured temperature of the switching voltage regulator 100 as part
of current estimation and over-temperature protection processes and
other control processes 126 implemented by the controller 106.
[0027] In one embodiment, the temperature compensation filter 120
generates a temperature-compensated total current estimate
(I.sub.T,comp) based on the total current estimate (I.sub.T)
generated by the current sensor 114 and a plurality of filter
coefficients that are a function of the measured temperature (T).
The filter coefficients are also a function of other parameters
related to the RC current sense networks 112, output inductors
(L.sub.O), and operation of the controller 106. These additional
parameters can be stored in data registers 128 of the controller
106. The temperature compensation filter 120 can mitigate
temperature-dependent measurement error during both steady-state
(DC) and transient (AC) conditions. For example, the temperature
compensation filter 120 can have a non-constant frequency response.
A digital embodiment of the temperature compensation filter 120 is
described in greater detail later herein with reference to FIG.
3.
[0028] The controller 106 further includes an over-temperature
protection circuit 130 that provides over-temperature protection
for the regulator 100. The over-temperature protection circuit 130
can shut down the switching voltage regulator 100 if regulator
operation cannot be maintained without exceeding some positive or
negative temperature limit. The over-temperature protection circuit
130 implements the over-temperature protection scheme based on the
same measured temperature (T) used to compensate for the
temperature variation between the DCR and inductance of the
inductor. This way additional temperature sensors for the phases
104 can be omitted, reducing system size and cost. Any standard
over-temperature protection circuit can be used.
[0029] FIG. 3 illustrates an embodiment of the temperature
compensation filter 120 included in or associated with the
switching voltage regulator controller 106. According to this
embodiment, the temperature compensation filter 120 is a digital
filter having a non-constant frequency response in order to
mitigate temperature-dependent measurement error during both
steady-state (or DC) and transient (or AC) conditions.
[0030] The temperature compensation filter 120 receives as inputs
the digitized total measured current (I.sub.T) generated by the
current sensor 114 and the digitized temperature reading (T)
measured by the temperature sensor 122. The temperature
compensation filter 120 also receives as inputs additional
parameters related to the RC current sense networks 112, output
inductors (L.sub.O), and operation of the controller 106, which can
be stored in data registers 128 of the controller 106.
[0031] The temperature compensation filter 120 implements a linear
first-order transfer function with a programmable gain, pole and
zero. The input of the filter 120 corresponds to the measured
voltage across the capacitor of an RC current sense network 112. If
the gain of the filter 120 is set to 1/DCR, the pole of the filter
120 is set to 1/RC, and the zero of the filter is set to DCR/L,
then the output of the filter 120 is a dynamically accurate
estimate of the current through the inductor. The programmable
gain, pole and zero can be varied over temperature such that those
values correspond to the temperature-dependent DCR, DCR/L, and RC
values. The ability to change the pole/zero placement of the filter
120 under nominal conditions means the time constant of the RC
current sense network 112 does not necessarily have to match the
time constant of the inductor and its DCR under nominal conditions.
The temperature compensation can be implemented using a look-up
table, piecewise linear, temperature slope compensation, or
higher-order function. The temperature compensation filter 120 thus
allows the controller 106 to estimate the current through the
inductor while compensating for temperature variation in the
system.
[0032] Coefficients (k.sub.1, k.sub.2) of the temperature
compensation filter 120 are determined as a function of the
parameters input to the filter 120. For example, the controller 106
calculates a first one (k.sub.1) of the filter coefficients as
given by:
k.sub.1=.tau..sub.C.DELTA..sub.T/.tau..sub.L. (1)
where .tau..sub.C=R.sub.sen.times.C.sub.sen,
.DELTA..sub.T=.alpha.(T-T.sub.0), .tau..sub.L=L.sub.O/DCR, .alpha.
is the temperature coefficient of resistivity of the material from
which the output inductor(s) are constructed (e.g. 0.0038/K for
copper), R.sub.sen is resistance of the resistor of the
corresponding RC current sense network 112, C.sub.sen is the
capacitance of the capacitor of the RC current sense network 112,
L.sub.O is the inductance of the corresponding inductor, and DCR is
the non-ideal DC resistance of the inductor (specified at nominal
conditions). The supplier of an inductor typically specifies the
DCR of the inductor in Ohms at a certain temperature e.g. 0.5
milliohms at 25.degree. C. As such, filter coefficient k.sub.1 is a
function of a time constant (.tau..sub.C) for the RC current sense
network 112 that measures the current through an output inductor of
the regulator 100, a time constant (.tau..sub.L) for the inductor
and a temperature parameter (.DELTA..sub.T) that is a function of a
difference between the measured temperature (T) and the temperature
(T.sub.0) at which the DCR of the inductor is specified. As such,
the controller 106 uses the measured temperature (T) to compensate
for the temperature variation between the DCR and inductance of the
inductor during both steady-state (or DC) and transient (or AC)
conditions.
[0033] The controller 106 calculates a second one (k.sub.2) of the
filter coefficients as given by:
k.sub.2=(1-(1+.DELTA..sub.T)/(F.sub.S.tau..sub.L) (2)
where F.sub.S is the sampling frequency at which the inductor
currents are estimated by the current sensor 114. The digital
temperature compensation filter 120 is implemented by the
controller 106 as shown in FIG. 3 using the filter coefficients
k.sub.1 and k.sub.2. For example, the temperature compensation
filter 120 can be implemented using a PID
(proportional-integral-derivative) controller where filter
coefficient k.sub.1 is used in the integral term (I) and filter
coefficient k.sub.2 is used in the derivative term (D). The
proportional term (P) can have unity gain or some other gain
value.
[0034] In general with regard to the temperature compensation
embodiment, the controller 106 generates a temperature-compensated
total current estimate (I.sub.T,comp) based on the total measured
current (I.sub.T) and the filter coefficients (k.sub.1, k.sub.2)
which are a function of the measured temperature (T). The
controller 106 can use the temperature-compensated total current
estimate to aid in various control functions 126 for the switching
voltage regulator 100 such as AVP (adaptive voltage positioning).
Dynamic voltage regulation of a switching voltage regulator can be
problematic. For example, many output capacitors can be used to
reduce voltage spikes that occur during transient periods. However,
increasing the number of output capacitors to meet high transient
requirements is not a suitable solution because of size and cost
issues. AVP is a more feasible way to dynamic voltage regulation.
The basic idea behind AVP is to control the output voltage level
(V.sub.O) so that it is slightly higher than a minimum value at
full load, and a little lower than a maximum value at light load.
As a result, the entire voltage tolerance window can be used for
voltage jumps or drops during transient periods.
[0035] The controller 106 can implement an AVP filter 300 that
filters the temperature-compensated total current estimate
(I.sub.T,comp) in order to provide dynamic voltage regulation. The
filtering implemented by the AVP filter 300 can be a function of
the load line (R.sub.LL) and bandwidth (.omega..sub.avp) of the AVP
filter 300 as shown in FIG. 3. The load line represents the
response of the linear part of the switching voltage regulator 100
connected to the (nonlinear) load. The output voltage level
(V.sub.O) of the switching voltage regulator 100 is controlled by
the AVP filter 300 so that the output voltage level is higher than
a minimum value at full load and lower than a maximum value at
light load. The controller 106 can use the temperature-compensated
total current estimate (I.sub.T,comp) to aid in still other control
functions 126 for the switching voltage regulator 100 such as
current balance and phase drop/add functions in the case of a
multiphase regulator.
[0036] FIG. 4 illustrates an embodiment of a current compensation
filter 400 for adjusting the estimate of the digitized current
estimate I.sub.T generated by the current sensor 114. According to
this embodiment, the current-dependency of the phase inductance is
used to implement the current estimate compensation. The structure
of the current compensation filter 400 shown in FIG. 4 is similar
to the structure of the temperature compensation filter 120 shown
in FIG. 3, however the filter coefficients are calculated
differently and there is a subtraction sign at the first
summation.
[0037] Coefficients (k.sub.1, k.sub.2) of the current compensation
filter 400 are determined as a function of the parameters input to
the filter 400. For example, the controller 106 calculates a first
one (k.sub.1) of the filter coefficients as given by:
k.sub.1=.tau..sub.C/.tau..sub..DELTA.I-1 (3)
where .tau..sub.C=R.sub.sen.times.C.sub.sen and
.tau..sub..DELTA.I=L(I)/DCR. L(I) is an estimate of the inductance
as a function of current and is given by:
L(I)=m.sub.LI+L.sub.b (4)
where m.sub.L is the slope of decrease for the inductance as a
function of current, I is current, and L.sub.b is the intercept of
the extrapolated slope for the inductance versus current. In one
embodiment, the current compensation filter 400 assumes a linear
decrease of inductance versus current i.e. m.sub.L is linear. FIG.
5 shows how the inductance of an inductor changes over current (L)
and temperature (.DELTA.T.degree. C.). The inductance is relatively
flat from 0 A to some current (I.sub.K), and then starts to decay
in a mostly linear manner.
[0038] The controller 106 calculates a second one (k.sub.2) of the
current compensation filter coefficients as given by:
k.sub.2=1/(1+1/(F.sub.S.tau..sub..DELTA.I)) (5)
where F.sub.S is the sampling frequency at which the inductor
currents are estimated by the current sensor 114. The digital
current compensation filter 400 is implemented by the controller
106 as shown in FIG. 4 using the filter coefficients k.sub.1 and
k.sub.2. For example, the current compensation filter 400 can be
implemented using a PID (proportional-integral-derivative)
controller where filter coefficient k.sub.1 is used in the integral
term (I) and filter coefficient k.sub.2 is used in the derivative
term (D). The proportional term (P) can have unity gain or some
other gain value. In one embodiment, the controller 106 can disable
the current compensation filter 400 over a range (L.sub.flat) of
the inductor current for which m.sub.L is relatively flat as shown
in FIG. 5. The filter 400 has no effect on the phase current
estimates when disabled. The filter 400 can be disabled by setting
the coefficients k.sub.1 and k.sub.2 to 1.
[0039] Terms such as "first", "second", and the like, are used to
describe various elements, regions, sections, etc. and are also not
intended to be limiting. Like terms refer to like elements
throughout the description.
[0040] As used herein, the terms "having", "containing",
"including", "comprising" and the like are open ended terms that
indicate the presence of stated elements or features, but do not
preclude additional elements or features. The articles "a", "an"
and "the" are intended to include the plural as well as the
singular, unless the context clearly indicates otherwise.
[0041] It is to be understood that the features of the various
embodiments described herein may be combined with each other,
unless specifically noted otherwise.
[0042] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that a variety of alternate and/or equivalent
implementations may be substituted for the specific embodiments
shown and described without departing from the scope of the present
invention. This application is intended to cover any adaptations or
variations of the specific embodiments discussed herein. Therefore,
it is intended that this invention be limited only by the claims
and the equivalents thereof.
* * * * *